As to conventional protection of a power switching circuit, protection against an overcurrent in an inverter is disclosed in, for example, Patent document 1. In this Patent document 1, when an overcurrent flows, a gate voltage control circuit operates so that an output interruption signal does not suddenly interrupt the overcurrent during its operation. Moreover, all switching elements are made turned off in the overcurrent protection operation.
In addition, for example, Patent document 2 describes a synchronous rectification system as driving a switching element to turn on, when an inductive load is driven, in the fly-back mode of a current flowing in the direction opposite to the forward direction of the switching element, and minimizing a voltage drop across the switching element. Moreover, it is also described that a dead time is shortened to a minimal level in this synchronous rectification system, whereby a free-wheel diode can be eliminated.
When an overcurrent exceeding a certain current level flows through a power semiconductor element, the element is likely to break down, so a function of protecting the element from the overcurrent is required. As the protection function against the overcurrent, a system is widely known in which the power semiconductor element includes a main switching element through which a main current flows and a sense switching element through which part of the main current flows, and the current flowing through the sense switching element is detected, thereby interrupting the main current. For example, a system is disclosed in Patent document 3, in which the gate of a main transistor, which is the main switching element, is separated from that of a sense transistor, which is the sense switching element; meanwhile, in the conventional example of Patent document 3 is also described such a case as a common gate being provided.